Carbon nanotube-coated optical fiber

Abstract

A carbon nanotube-coated optical fiber comprising an optical fiber and a carbon nanotube fibrous layer coating the surface of the optical fiber.

Description

Carbon nanotube-coated optical fiber Cross-reference to related applications 【0001】 This application claims priority based on Japanese Patent Application No. 2024-213908 filed on December 6, 2024, and incorporates all the descriptions set forth in the Japanese application. 【0002】 This disclosure relates to carbon nanotube-coated optical fibers. 【0003】 Conventionally, resin-coated optical fibers in which an optical fiber is coated with a resin such as an acrylic resin and a polyimide resin, or metal-coated optical fibers in which an optical fiber is coated with a metal such as copper and titanium are widely used. There are also cases where a coated optical fiber having a resin layer and a metal layer is used (see, for example, Patent Document 1). 【0004】 Japanese Patent Application Laid-Open No. 2007-003670 【0005】 When a resin-coated optical fiber is heated to about 400°C or higher, the resin may melt, and there is room for improvement in heat resistance in the resin-coated optical fiber. Further, when a metal-coated optical fiber is heated to about 500°C or higher, the metal may thermally expand and peel off, or the optical fiber may break due to the thermal stress of the metal, and there is also room for improvement in heat resistance in the metal-coated optical fiber. Therefore, an object of the present disclosure is to provide a coated optical fiber having excellent heat resistance. 【0006】 One aspect of the coated optical fiber of the present disclosure includes an optical fiber and a carbon nanotube fiber layer that coats the surface of the optical fiber. 【0007】 The carbon nanotube-coated optical fiber of the present disclosure has excellent heat resistance. 【0008】Figure 1 is a top view of a carbon nanotube forest and a carbon nanotube web illustrating a method for manufacturing a carbon nanotube web. Figure 2 is a cross-sectional view taken along line AA in Figure 1. Figure 3A is a schematic diagram illustrating a method for forming a carbon nanotube fiber layer. Figure 3B is a schematic diagram illustrating a method for forming a carbon nanotube fiber layer. Figure 4A is a schematic diagram illustrating the orientation angle in a carbon nanotube fiber layer. Figure 4B is a schematic diagram illustrating the orientation angle, the distance between the centerlines of the bundle, the width of the bundle, and the spacing between the bundles in a bundle of carbon nanotube fibers covering an optical fiber. Figure 5 is a diagram showing a carbon nanotube-coated optical fiber (1) in Example 1 fixed on a heat-resistant metal plate. 【0009】 Hereinafter, an example of an embodiment of this disclosure will be described in detail with reference to the drawings. Note that, for convenience, the drawings used in the following description may show enlarged versions of characteristic parts to make the features of this disclosure easier to understand. Therefore, the dimensional ratios of each component may differ from those of the actual components. In this specification, the numerical range A to B means A or greater and B or less. In this specification, if the units of the numerical values ​​before and after the "~" indicating a numerical range are the same, the unit of the numerical value before the "~" may be omitted. Throughout this specification, singular expressions should be understood to include the concept of their plural form unless otherwise specified. Therefore, singular articles (for example, "a," "an," and "the" in English) should be understood to include the concept of their plural form unless otherwise specified. Furthermore, terms used in this specification should be understood to have the meaning commonly used in the art unless otherwise specified. The upper and / or lower limits of the numerical ranges described in this specification can be arbitrarily combined to define a preferred range. For example, a preferred range can be defined by arbitrarily combining the upper and lower limits of a numerical range, a preferred range can be defined by arbitrarily combining the upper limits of a numerical range, and a preferred range can be defined by arbitrarily combining the lower limits of a numerical range. 【0010】In the following explanation, the terms "film" and "sheet" are not clearly distinguished; the term "film" may include "sheet," and vice versa. 【0011】 In this specification, "parallel" includes not only strictly parallel but also approximately parallel. For parallel lines, the angle between them may be, for example, 30° or less, 20° or less, 10° or less, or 5° or less. In this specification, "perpendicular" includes not only strictly perpendicular but also approximately perpendicular, and "orthogonal" includes not only strictly orthogonal but also approximately orthogonal. For perpendicular and orthogonal lines, the angle between them may be, for example, 60° or more and 90° or less, 70° or more and 90° or less, 80° or more and 90° or less, or 85° or more and 90° or less. 【0012】 Hereinafter, carbon nanotubes will also be referred to as "CNT," carbon nanotube-based materials as "CNT-based materials," fibers composed of carbon nanotubes directly extracted from a carbon nanotube forest as "CNT fibers," threads composed of CNT fibers as "CNT threads," a web-like structure of carbon nanotubes as "CNT webs," and a film of carbon nanotubes as "CNT films." 【0013】 [Carbon Nanotube Coated Optical Fiber] The carbon nanotube coated optical fiber (CNT coated optical fiber) of this disclosure comprises an optical fiber and a carbon nanotube fiber layer (CNT fiber layer). The CNT fiber layer coats the surface of the optical fiber. 【0014】 <Optical Fiber> The CNT-coated optical fiber of this disclosure comprises an optical fiber. Examples of optical fibers include glass optical fibers such as quartz glass fibers, and plastic optical fibers. The optical fiber may include a core and a cladding. 【0015】Examples of materials used to form the core of an optical fiber include glass and resin. Examples of glass include quartz glass, fluoride glass, chalcogenide glass, borate glass, phosphate glass, germanate glass, sapphire glass, and silicate glass. As for the glass, glass with low optical loss is preferred, and quartz glass is preferred, for example. 【0016】 Examples of the above-mentioned resins include polymethyl methacrylate resins and polycarbonate resins. The above-mentioned glass and resin may be used individually or in combination of two or more types. 【0017】 Examples of materials used to form the cladding of optical fibers include glass and resin. Examples of glass include the same types of glass mentioned as materials for forming the core. 【0018】 Examples of the above-mentioned resins include fluororesins. Examples of fluororesins include fluorinated (meth)acrylate polymers and polyvinylidene fluoride polymers. 【0019】 The refractive index of the cladding material may be lower than that of the core material. The same material may be used for both the core and the cladding. 【0020】 An optical fiber may contain one core or multiple cores. A cladding may contain one core or multiple cores. 【0021】The diameter of an optical fiber varies depending on its application, but is, for example, 80 nm to 500 μm. In one embodiment, the diameter of the optical fiber is preferably 20 to 500 μm, more preferably 100 to 200 μm. Having the diameter of the optical fiber within this range is preferable, for example, when using the optical fiber for communication applications. In another embodiment, the diameter of the optical fiber is preferably 80 nm to 100 μm, more preferably 100 nm to 80 μm. Having the diameter of the optical fiber within this range is preferable, for example, when using the optical fiber for sensing applications. The diameter of the optical fiber is measured by observing a cross-section perpendicular to its long axis using a scanning electron microscope (SEM) or optical microscope, or by using calipers. The length of the optical fiber is not particularly limited and can be set according to the application of the CNT-coated optical fiber. 【0022】 A CNT-coated optical fiber may consist of one optical fiber or multiple optical fibers. 【0023】 As optical fibers, commercially available products with a surface coating of resin or the like may be provided, or optical fibers without a surface coating may be provided. When using optical fibers with a surface coating, the coating is affected by heat, so if optical fibers with a surface coating are provided, it is preferable to remove the surface coating from the optical fiber before use. 【0024】 <Carbon Nanotube Fiber Layer> The CNT-coated optical fiber of this disclosure comprises a carbon nanotube fiber layer (CNT fiber layer). The CNT fiber layer includes a CNT-based material. The CNT-based material is not particularly limited as long as it is a material that includes CNT fibers or aggregates thereof. Examples of CNT-based materials include CNT fibers and CNT yarns. 【0025】The thickness of the CNT fiber layer is preferably 1 to 50 μm, more preferably 1 to 30 μm, even more preferably 2 to 15 μm, and particularly preferably 3 to 9 μm, from the viewpoint of heat resistance, flexibility, and adhesion to the optical fiber. The average thickness of the CNT fiber layer is measured by observing a cross-section perpendicular to the long axis of the CNT-coated optical fiber using a scanning electron microscope (SEM). 【0026】 Since the CNT fiber layer is presumed to maintain high surface energy due to the van der Waals forces of the CNTs, the CNT fiber layer adheres well to the optical fiber even if there is no adhesive layer between the CNT fiber layer and the optical fiber in the CNT-coated optical fiber. 【0027】 The CNT fiber layer may cover a single optical fiber, or it may cover multiple optical fibers together. Multiple optical fibers, each covered by a CNT fiber layer, may be gathered together and then further covered by a different CNT fiber layer. 【0028】 CNTs can be manufactured using conventionally known methods. For example, CNTs can be manufactured using methods such as thermochemical vapor deposition (thermal CVD), plasma CVD, laser ablation, arc discharge, or combustion. 【0029】 The carbon purity of CNTs is preferably 95.0 to 99.999%. The lower limit of carbon purity of CNTs is preferably 96.0%, more preferably 97.0%, even more preferably 98.0%, even more preferably 99.0%, and particularly preferably 99.8%. The upper limit of carbon purity of CNTs may be, for example, 99.99% or 99.9%. The carbon purity of CNTs can be determined, for example, by elemental analysis using X-ray fluorescence. 【0030】 The crystallinity of carbon nanotubes (CNTs) can be evaluated, for example, using Raman spectroscopy. In Raman spectroscopy, the D / G ratio is used as an indicator for evaluating crystallinity. The D / G ratio is the value at 1580 cm⁻¹ in the Raman spectrum measured by Raman spectroscopy. -1 1360 cm⁻¹ relative to the peak intensity of the G-band appearing in the vicinity -1This is the ratio of the peak intensities of the D-band that appear in the vicinity. A smaller D / G ratio indicates higher crystallinity of the carbon nanotube. The D / G ratio in CNTs is preferably 0.5 to 1.0, more preferably 0.6 to 0.8. 【0031】 The carbon purity and crystallinity of the CNTs can be adjusted, for example, by adjusting the thickness of the buffer layer in the catalyst substrate, the type of material used for the buffer layer, the thickness of the catalyst layer, the type of catalyst, the type and flow rate of the raw material gas in the CVD method, and the temperature and pressure in the reaction chamber, as described later. 【0032】 The CNTs may be single-walled carbon nanotubes or multi-walled carbon nanotubes with two or more layers. Preferably, the CNTs are multi-walled carbon nanotubes. The number of layers in the multi-walled carbon nanotubes is not particularly limited, but is preferably 2 to 20. 【0033】 The average length of the CNTs is preferably 10 to 1000 μm, more preferably 30 to 800 μm, and even more preferably 50 to 500 μm. The average length of the CNTs can be adjusted, for example, by adjusting the time spent on the CVD process, i.e., the CNT growth time. The average diameter of the CNTs is preferably 1 to 50 nm, more preferably 3 to 30 nm, and even more preferably 5 to 15 nm. The average diameter of the CNTs can be adjusted, for example, by adjusting the thickness of the catalyst layer and the type of catalyst, as described later. 【0034】 The average length and average diameter of a carbon nanotube (CNT) are measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Specifically, ten images of the CNT are obtained using an SEM or TEM. Ten length measurement points are arbitrarily selected from each of the ten images and measured, totaling 100 lengths. The average length of the CNT is then calculated by arithmetic mean of these 100 length measurements. Similarly, ten diameter measurement points are arbitrarily selected from each of the ten images and measured, totaling 100 diameters. The average diameter of the CNT is then calculated by arithmetic mean of these 100 diameter measurements. 【0035】CNT fibers refer to fibers containing multiple carbon nanotubes (CNTs). In CNT fibers, multiple CNTs are oriented in one direction. In CNT fibers, the longitudinal directions of the multiple CNTs are aligned in one direction. CNT fibers can be manufactured by extracting multiple CNTs from a carbon nanotube forest (CNT forest). 【0036】 CNT yarn may be, for example, a linear body obtained by bundling multiple CNT fibers (CNT webs) drawn out in a sheet-like manner from a CNT forest, or a twisted yarn obtained by twisting the linear body. CNT yarn can also be obtained, for example, by spinning using a dispersion of CNTs. The above-mentioned multiple CNT fibers constitute a CNT web. 【0037】 The average diameter of the CNT yarn is preferably 1 nm to 2 mm, more preferably 100 nm to 100 μm, and even more preferably 1 to 30 μm. The average diameter of the CNT yarn is measured by the same method as the average diameter of the CNTs. 【0038】 A CNT forest refers to an aggregate of multiple CNTs arranged on a substrate and oriented perpendicular to the substrate surface. In a CNT forest, multiple CNTs stand upright on the substrate. 【0039】 A CNT forest can be obtained, for example, by performing chemical vapor deposition (CVD) on a catalyst substrate comprising a substrate and a catalyst layer provided on the substrate. The CVD method involves placing the catalyst substrate in a reaction chamber, supplying a raw material gas to the reaction chamber, and growing CNTs on the surface of the catalyst layer. Thermal CVD is preferred as the CVD method. 【0040】 Examples of substrates include silicon substrates, alumina substrates, magnesium oxide substrates, glass substrates, sapphire substrates, and stainless steel substrates. 【0041】The catalyst layer can be formed, for example, by attaching catalyst particles to a substrate by sputtering. Examples of the catalyst include metals, specifically, iron (Fe), nickel (Ni), cobalt (Co), molybdenum (Mo), gold (Au), and alloys containing at least one metal selected from the group consisting of these. Examples of the alloy include iron alloys, nickel alloys, and cobalt alloys. The catalyst may be a metal precursor such as a metal oxide and a metal compound. Examples of the metal oxide include iron oxide, nickel oxide, and cobalt oxide. Examples of the metal compound include iron chloride. When using a precursor, it is necessary to convert it to a metal before performing the CVD method, such as by heating the precursor. 【0042】 The catalyst substrate may further include a buffer layer between the substrate and the catalyst layer. Examples of the material used for the buffer layer include silica (SiO2), alumina (Al2O3), silicon nitride (SiN), zinc oxide (ZnO), copper oxide (Cu2O), and nickel oxide (NiO). The buffer layer can be formed, for example, by sputtering. 【0043】 Sputtering for forming the catalyst layer and sputtering for forming the buffer layer can be performed using known apparatuses and conditions according to the sputtering target. The pressure condition for performing sputtering is preferably 0.01 to 10 Pa, more preferably about 0.1 to 1 Pa. 【0044】As the raw material gas, a raw material gas containing carbon can be used. For example, hydrocarbons, sulfur-containing organic gases, phosphorus-containing organic gases, carbon monoxide, and alcohols can be mentioned. Examples of hydrocarbons include alkane compounds such as methane and ethane, alkene compounds such as ethylene and butadiene, alkyne compounds such as acetylene, aryl hydrocarbon compounds such as benzene, toluene, and styrene, aromatic hydrocarbons having condensed rings such as indene, naphthalene, and phenanthrene, cycloalkane compounds such as cyclopropane and cyclohexane, cycloolefin compounds such as cyclopentene, and alicyclic hydrocarbon compounds having condensed rings such as steroids. Examples of alcohols include methanol and ethanol. From the perspective of the carbon purity of the obtained CNT, the raw material gas is preferably a hydrocarbon. 【0045】 A carrier gas, which is a gas for transporting the raw material gas, may be supplied to the reaction chamber together with the raw material gas. Examples of the carrier gas include helium, neon, argon, nitrogen, and hydrogen. 【0046】 From the perspective of the growth rate of CNTs and the carbon purity of the obtained CNTs, the temperature in the reaction chamber in the CVD method is preferably 600 to 850 °C, more preferably 650 to 800 °C. From the perspective of the growth rate and carbon purity of CNTs, the pressure in the reaction chamber in the CVD method is preferably normal pressure. Depending on other conditions when implementing the CVD method, the pressure in the reaction chamber may be reduced or increased from normal pressure. 【0047】 The average length and average diameter of the CNTs in the CNT forest are, for example, the same as the average length and average diameter of the CNTs described above, respectively. 【0048】The CNT fiber layer is preferred because it has excellent heat resistance, is less susceptible to thermal expansion compared to metals, is dense, and has excellent adhesion to the optical fiber. The CNT fiber layer is a layer containing CNT fibers, for example, a layer formed by wrapping CNT fibers or CNT yarn, preferably CNT fibers, around the surface of an optical fiber. Examples of CNT fiber layers include a layer formed by wrapping a plurality of CNT fibers (CNT webs) or bundles thereof, drawn out in a sheet-like form from a CNT forest, around the surface of an optical fiber, and a layer formed by covering the surface of an optical fiber with a sheet-like body of CNT-based material. Examples of layers formed by wrapping a bundle of the plurality of CNT fibers (CNT webs) around the surface of an optical fiber include a layer formed by wrapping a linear body obtained by bundling the plurality of CNT fibers around the surface of an optical fiber, and a layer formed by wrapping a twisted yarn-like body obtained by twisting the plurality of CNT fibers or the linear body around the surface of an optical fiber. The surface of the optical fiber refers to the outer periphery of the optical fiber surface. 【0049】 From the viewpoint of being dense and having excellent adhesion to optical fibers, the CNT fiber layer is preferably a layer formed by wrapping multiple CNT fibers or bundles thereof, which are drawn out in a sheet-like form from a CNT forest, around the surface of an optical fiber. 【0050】 The orientation angle (angle θ shown in Figures 4A and 4B), which is the angle between the optical fiber and the CNT fiber or CNT thread, is preferably 0.8 to 70°, more preferably 1.6 to 60°. The closer the orientation angle approaches 45°, the better the mechanical properties of the CNT-coated optical fiber tend to be. The orientation angle is measured by observing the surface of the CNT-coated optical fiber with an optical microscope or the like. 【0051】<Manufacturing of CNT-Coated Optical Fibers> CNT-coated optical fibers can be manufactured, for example, by a method that includes a step of winding CNT fibers around the surface of an optical fiber. Specifically, CNT-coated optical fibers can be manufactured by a method that includes a step of attaching a plurality of CNT fibers or bundles drawn from a CNT forest to the surface of an optical fiber, and then rotating the CNT forest around the optical fiber to coat the surface of the optical fiber with CNT fibers; a method that includes a step of winding a sheet-like body of CNT-based material around an optical fiber; or a method that includes a step of attaching a plurality of CNT fibers or bundles drawn from a CNT forest to the surface of an optical fiber, and then rotating the optical fiber in the longitudinal direction (rotating the optical fiber) to coat the surface of the optical fiber with CNT fibers. 【0052】 CNT-coated optical fibers are preferably manufactured by a method that includes the step of winding a plurality of CNT fibers or bundles drawn from a CNT forest onto an optical fiber to form a CNT fiber layer. In the above step, it is preferable that after the CNT fibers or bundles are attached to the surface of the optical fiber, the CNT forest is rotated around the optical fiber to coat the surface of the optical fiber with CNT fibers. Since the CNT fibers drawn from the CNT forest maintain high surface energy, the CNT fibers can adhere to the optical fiber without the use of adhesives or the like. 【0053】 Specifically, a CNT-coated optical fiber can be manufactured by a method comprising: a step of unwinding an optical fiber; a step of winding a plurality of CNT fibers or bundles drawn from a CNT forest onto the optical fiber to form a CNT fiber layer and obtain a CNT-coated optical fiber; and a step of winding up the CNT-coated optical fiber. 【0054】CNT fibers or CNT webs can be manufactured, for example, by using a gripping tool such as tweezers to pull out CNTs located at the ends of a CNT forest so that they are separated from the CNT forest in a direction parallel to the surface of the substrate on which the CNT forest is provided. When CNTs located at the ends of a CNT forest are pulled out, adjacent CNTs are sequentially pulled out by van der Waals forces. The pulled-out CNTs are oriented so that their longitudinal direction aligns with the direction from which they were pulled. Therefore, the multiple CNTs constituting the CNT fiber are oriented in one direction. The multiple CNTs constituting the CNT fiber are bonded to each other by van der Waals forces. 【0055】 An example of a method for manufacturing CNT fibers or CNT webs will be explained with reference to the drawings. Figure 1 is a top view illustrating the process of manufacturing a CNT web 20 containing a plurality of CNT fibers 22 using a CNT substrate 10 equipped with a CNT forest 12 provided on a substrate 11, and Figure 2 is a cross-sectional view taken along line AA in Figure 1. 【0056】 The CNT web 20 shown in Figures 1 and 2 can be manufactured by pulling out a plurality of CNTs located at the ends of a CNT forest 12 provided on a substrate 11 and oriented perpendicular to the surface of the substrate 11, in a sheet-like manner in a direction parallel to the surface of the substrate 11, away from the CNT forest 12. In Figure 1, a plurality of CNT fibers 22 (i.e., CNT web 20) manufactured by pulling out a plurality of CNTs from the CNT forest 12 are bundled at their tip and attached to an optical fiber 2. 【0057】 Figures 3A and 3B show an example of a method for coating an optical fiber using multiple CNT fibers. An optical fiber 2, a substrate 11, and a CNT substrate 10 comprising a CNT forest 12 provided on the substrate 11 are prepared. 【0058】The optical fiber 2 is positioned to extend along the X-axis. For example, the optical fiber 2 is partially unwound from a winding body wound on a first roll (not shown) and fixed or wound onto a second roll (not shown). The unwound optical fiber 2 extends along the X-axis with little to no slack between the first and second rolls, for example. Next, a plurality of CNT fibers 22 (CNT web 20) or bundles drawn out in a sheet-like manner from the CNT forest 12 are attached to the surface of the unwound optical fiber 2. 【0059】 Next, the optical fiber 2 is moved in the positive direction of the X-axis over time. For example, this movement of the optical fiber 2 is achieved by unwinding the optical fiber 2 from the first roll and winding it onto the second roll. The CNT substrate 10 is also rotated around the optical fiber 2, using the optical fiber 2 extending in the X-axis direction or an axis parallel to it as the axis of rotation. In Figures 3A and 3B, the CNT substrate 10 rotates along the dashed line R. As a result, the CNT fibers 22 or bundles obtained from the CNT forest 12 wrap around the surface of the optical fiber 2, and the position where they wrap (coating position) on the optical fiber 2 moves. Thus, a CNT fiber layer 4 covering the optical fiber 2 is formed, and a CNT-coated optical fiber 1 is obtained. The CNT fibers 22 or bundles cover the optical fiber 2, for example, in a spiral shape. The CNT-coated optical fiber 1 is wound onto, for example, the second roll. 【0060】 It is preferable to adjust the moving speed of the optical fiber 2 (linear speed of the optical fiber 2, unwinding speed of the optical fiber 2, or winding speed of the CNT-coated optical fiber 1) in accordance with the rotation speed of the CNT substrate 10. For example, it is preferable to synchronize the rotation speed and the moving speed. This synchronization makes it possible to form a dense CNT fiber layer 4 with excellent adhesion to the optical fiber 2. By adjusting the rotation speed and the moving speed, for example, the orientation angle, which is the angle between the CNT fiber and the optical fiber, can be controlled. If the rotation speed and the moving speed are kept constant, the orientation angle can be kept constant. If the rotation speed and / or the moving speed are changed while coating is being applied, the orientation angle can be changed without stopping the coating process. 【0061】 After the CNT fiber layer 4 is formed, the CNT-coated optical fiber 1 may be brought into contact with a solvent, and then the solvent may be removed. Contact may be performed by immersing the CNT-coated optical fiber 1 in the solvent, by spraying the solvent, by applying the solvent, or by dropping the solvent. As the solvent, a solvent that vaporizes easily can be used. Examples of such solvents include lower alcohols such as ethanol and organic solvents such as acetone. It is preferable to bring the CNT-coated optical fiber 1 into contact with a solvent and remove the solvent by vaporization, as this tends to improve the adhesion between the CNT fiber layer 4 and the optical fiber 2. 【0062】 Figure 4B shows an example of a CNT-coated optical fiber 1 (side view of the CNT-coated optical fiber 1) obtained when the rotational speed of the CNT substrate 10, the moving speed of the optical fiber 2, and the width of the bundle of CNT fibers 22 that spirally covers the optical fiber 2 (L0 in Figure 4B) are kept constant. In Figure 4B, a part of the CNT-coated optical fiber 1 is shown in an enlarged view. When the angular velocity of the CNT substrate 10 is w (rad / sec), the thickness (diameter) of the optical fiber 2 is 2r (m), the moving speed of the optical fiber 2 is v (m / sec), and the distance between the centerlines of the bundle that spirally covers the optical fiber 2 is L (m), then w, r, v and L have the relationship given by equation (I) below, and w, r, v and the orientation angle θ have the relationship given by equation (II) below. 【0063】 【0064】 【0065】 Furthermore, if the width of the bundle that spirally covers the optical fiber 2 is L0 (m), the spacing ΔL (m) between adjacent bundles on the optical fiber 2 is expressed by the following equation (III). 【0066】 【0067】In equation (III), w, r, and v are the same as in equation (I). When ΔL is positive, adjacent bundles on the optical fiber 2 do not overlap, and the bundles cover the optical fiber 2 in such a way that there are gaps between them. When ΔL is negative, adjacent bundles cover the optical fiber 2 in such a way that they overlap. ΔL is preferably 0 or negative. 【0068】 The angular velocity of the CNT substrate 10 is preferably 0.1 to 12.6 rad / second, more preferably 0.3 to 9.4 rad / second, and even more preferably 0.5 to 6.3 rad / second. In one preferred embodiment, the CNT substrate 10 rotates (revolves) along a circle with a radius of 1 cm to 1 m. In another preferred embodiment, the CNT substrate 10 rotates (revolves) along a circle with a radius of α + 0.5 cm to α + 1 m. In a more preferred embodiment, the CNT substrate 10 rotates (revolves) along a circle with a radius of α + 1 cm to α + 50 cm. α refers to the thickness of the optical fiber 2. For example, if the optical fiber 2 has a thickness of 80 μm to 1 cm, and the dashed line R in Figures 3A and 3B is a circle with a radius of 3 cm, that is, if the CNT substrate 10 is rotated along the circumference of a circle with a radius of 3 cm, the rotation speed of the CNT substrate 10 is preferably 100 to 1000 cm / min, more preferably 150 to 800 cm / min, and even more preferably 180 to 600 cm / min. 【0069】 The moving speed of the optical fiber 2 is preferably 0.1 to 20 cm / min, more preferably 0.5 to 15 cm / min, and even more preferably 0.8 to 12 cm / min. The orientation angle is preferably 0.8 to 70°, more preferably 1.6 to 60°. The mechanical properties of the CNT-coated optical fiber tend to improve as the orientation angle approaches 45°. The orientation angle is measured by observing the surface of the CNT-coated optical fiber with an optical microscope or the like. 【0070】For example, the width of the CNT substrate 10 required to cover a 1 cm diameter optical fiber 2 with an orientation angle of approximately 45° (the length of the CNT forest 12 in the direction in which the multiple CNT fibers 22 constituting the CNT web 20 are aligned when the CNT web 20 is drawn out from the CNT forest 12, i.e., length d in Figure 1) is preferably 1 to 10 cm, more preferably 2 to 8 cm, and even more preferably 3 to 5 cm, and it is preferable to adjust the rotation speed of the CNT substrate 10 and the movement speed of the optical fiber 2 within the above range. The dashed line R is preferably a circle with a radius of 1 cm to 1 m. 【0071】 From the viewpoint of designability of the manufacturing apparatus for the CNT-coated optical fiber 1 and ease of formation of the CNT fiber layer 4, it is preferable to arrange the CNT substrate 10 so that the CNT forest 12 faces the optical fiber 2 side and the substrate 11 faces outward, and then rotate it. 【0072】 The CNT web 20 may be drawn from one location in the CNT forest 12 and the bundle may be attached to the optical fiber 2, or the CNT web 20 may be drawn from multiple locations in the CNT forest 12 and the bundle may be attached to the optical fiber 2. 【0073】More than one CNT substrate 10 may be used. That is, two or more CNT substrates 10 (for example, a first and a second CNT substrate) may be rotated around the optical fiber 2, using the optical fiber 2 extending in the X-axis direction or an axis parallel to it as the axis of rotation. In this case, a plurality of CNT fibers 22 (CNT webs 20) or bundles drawn from the CNT forest 12 of the first CNT substrate are attached to the surface of the unwound optical fiber 2, and a plurality of CNT fibers 22 (CNT webs 20) or bundles drawn from the CNT forest 12 of the second CNT substrate are attached to the surface of the unwound optical fiber 2. As a result, the CNT fibers 22 or bundles obtained from the CNT forest 12 of the first CNT substrate are wrapped around the surface of the optical fiber 2, and the CNT fibers 22 or bundles obtained from the CNT forest 12 of the second CNT substrate are wrapped around the surface of the optical fiber 2, forming a CNT fiber layer 4 that covers the optical fiber 2. The number of CNT substrates can be, for example, 1 to 5, 1 to 3, or 1 to 2. Alternatively, the CNT substrate 10 itself may be cylindrical, and the CNT forest 12 may surround the optical fiber 2 in a 360-degree configuration. 【0074】 The CNT fiber layer may be a layer formed by covering the surface of an optical fiber with a sheet-like body of CNT-based material, for example. For example, the CNT fiber layer may be formed by winding the sheet-like body around an optical fiber. Examples of the sheet-like body include fabrics of CNT fibers or CNT yarns, nonwoven fabrics of CNT fibers or CNT yarns, CNT webs, and CNT films. 【0075】 Examples of fabrics made from CNT fibers or CNT yarns include plain weave, twill weave, or satin weave fabrics. As nonwoven fabrics made from CNT fibers or CNT yarns, for example, conventionally known nonwoven fabrics obtained using CNT fibers or CNT yarns can be used. 【0076】A CNT web refers to a web containing multiple CNT fibers. A CNT web may also be an aggregate of multiple CNT fibers that, when viewed from above, extend in one direction and are arranged perpendicular to that direction. "Viewing a CNT web from above" means viewing a planar CNT web from its normal direction. 【0077】 The CNT web may be an aggregate in which, when viewed from above, a plurality of CNT fibers extend along a first direction and are arranged perpendicular to the first direction, and a plurality of CNT fibers extend along a second direction and are arranged perpendicular to the second direction, and the first direction and the second direction intersect. The angle between the first direction and the second direction is not particularly limited. The first direction and the second direction may be orthogonal, for example. The CNT web may further include an nth fiber group (n is an integer of 3 or more) in which a plurality of CNT fibers extend along an nth direction and are arranged perpendicular to the nth direction. 【0078】 A CNT web can be manufactured, for example, by extracting multiple CNTs from a CNT forest, specifically by extracting multiple CNTs in a sheet-like form. The size of the CNT web can be adjusted by adjusting the width of the CNTs extracted from the CNT forest. 【0079】 The CNT web is preferably a CNT web obtained by drawing out multiple CNTs from a CNT forest provided on a substrate, or a laminate of said CNT web. Here, the CNT web is, for example, an aggregate in which, when viewed from above, multiple CNT fibers extend along one direction and are arranged perpendicular to that direction. Hereinafter, the direction in which the CNT fibers extend in the CNT web will also be referred to as the "longitudinal direction of the CNT fibers". 【0080】A CNT web may be manufactured, for example, by bringing a rectangular instrument into contact with the side wall or the upper surface of the end of a CNT forest, which constitutes the CNT forest, and moving the instrument away from the CNT forest in a direction parallel to the surface of the substrate on which the CNT forest is provided. 【0081】 A laminate of CNT webs can be manufactured, for example, by producing multiple sheets of CNT webs obtained by extracting multiple CNTs from a CNT forest, and then laminating each CNT web, or by manufacturing a roll by winding multiple CNT webs obtained by extracting multiple CNTs from a CNT forest around the circumferential surface of a roller, and then cutting open the roll along the rotation axis of the roller. In the latter method, the number of layers of the CNT web is the number of turns when the CNT web is wound around the roller. 【0082】 When manufacturing a laminate of CNT webs by first manufacturing multiple CNT webs in sheet form and then stacking them, the CNT webs may be stacked so that the longitudinal direction of the CNT fibers constituting one CNT web is parallel to the longitudinal direction of the CNT fibers constituting another CNT web, or they may be stacked so that they intersect (for example, orthogonally). 【0083】 The CNT film may be, for example, a laminate of the CNT web described above. The CNT film may also be, for example, a laminate of CNT webs in which CNT webs are laminated so that the CNT fibers are parallel. 【0084】 CNT films can also be obtained, for example, by manufacturing multiple CNT fibers, assembling them, and then applying pressure to the CNT fiber aggregate to bond the CNT fibers together. The CNT film obtained by this method is typically a film composed of CNT fibers. 【0085】 There are no particular restrictions on the basis weight of the sheet-like material made of CNTs, but from viewpoints such as productivity, it is preferably 0.02 to 170 mg / cm². 2 More preferably 0.03 to 85 mg / cm² 2More preferably 0.05 to 17 mg / cm³ 2 The above basis weight can be determined by measuring the mass of the CNT material using a balance or other scale and dividing the mass by the area of ​​the material. When the sheet-like body of the CNT material is a laminate of CNT webs, the number of CNT web layers in the laminate is preferably 20 to 10,000, more preferably 30 to 5,000, and even more preferably 50 to 1,000. 【0086】 <Effects and Applications of CNT-Coated Optical Fibers> It is preferable that CNT-coated optical fibers do not have a coating layer containing resin and / or metal. CNTs are stable up to approximately 500°C in environments such as air containing oxygen, and stable up to approximately 3000°C in environments without oxygen. For this reason, CNT-coated optical fibers can be used in high-temperature environments up to approximately 500°C in environments such as air containing oxygen. Furthermore, in environments without oxygen, CNT-coated optical fibers can be used in ultra-high-temperature environments up to approximately 1700°C, depending on the heat resistance of the optical fiber, for example, when using quartz glass fiber. In CNT-coated optical fibers, because the optical fiber is coated only with a CNT fiber layer, even if the CNT-coated optical fiber is heated to a high temperature of approximately 400°C or higher, there is little risk of the coating layer melting or carbonizing, and there is also little risk of the coating layer delaminating due to thermal expansion or the optical fiber breaking due to thermal stress on the coating layer. Therefore, CNT-coated optical fibers have excellent heat resistance. In particular, in oxygen-free environments, the upper limit of the usable temperature range for CNTs is generally higher than that of glass fibers. Therefore, CNT-coated optical fibers can be used as long as they are within the usable temperature range of glass fibers. 【0087】CNT-coated optical fibers can be used in environments such as high-temperature and high-pH environments. CNT-coated optical fibers are used, for example, in optical fiber sensing equipment. An optical fiber sensing device comprises, for example, a CNT-coated optical fiber and an optical fiber measuring instrument. The optical fiber sensing device may have only one CNT-coated optical fiber or multiple CNT-coated optical fibers. An optical fiber sensing device equipped with a CNT-coated optical fiber is used for optical fiber sensing, and is particularly suitable for optical fiber sensing in extreme environments. The above-mentioned optical fiber sensing device can be used, for example, for sensing applications in oil or gas plants, power plants, power transmission and distribution lines and other power facilities, boilers, and solid oxide fuel cells. Sensing using a CNT-coated optical fiber allows for the measurement of, for example, temperature, strain, and pressure. 【0088】 CNT-coated optical fibers are used, for example, in distributed optical fiber sensors, optical fiber sensors using Fabry-Perot interferometers, and fiber Bragg grating (FBG) sensors. Examples of sensing methods using distributed optical fiber sensors include the Optical Frequency Domain Reflectometry (OFDR) method, the Optical Time Domain Reflectometry (OTDR) method, the Raman OTDR (ROTDR) method, the Brillouin OTDR (BOTDR) method, and the Distributed Acoustic Sensing (DAS) method. CNT-coated optical fibers may also be used for applications other than sensing, such as communication applications. 【0089】 CNT-coated optical fibers can be used not only in air and vacuum, but also in environments containing nitrogen, hydrogen, or acetylene. Furthermore, because CNTs are hydrophobic, CNT-coated optical fibers can be used in humid environments as well. 【0090】 Because the CNT-coated optical fiber has a CNT fiber layer, it maintains high bending strength even when, for example, the CNT-coated optical fiber is heated to a high temperature and then cooled to room temperature. 【0091】 This disclosure relates, for example, to the following [1] to [4]: ​​[1] A carbon nanotube coated optical fiber comprising: an optical fiber and a carbon nanotube fiber layer covering the surface of the optical fiber. [2] The carbon nanotube coated optical fiber according to [1], wherein the thickness of the carbon nanotube fiber layer is 1 to 50 μm. [3] The carbon nanotube coated optical fiber according to [1] or [2], wherein the optical fiber is a quartz glass fiber. [4] An optical fiber sensing device comprising the carbon nanotube coated optical fiber according to any one of [1] to [3]. 【0092】 The CNT-coated optical fiber of this disclosure will be described in more detail below based on the examples, but the CNT-coated optical fiber of this disclosure is not limited to the examples. 【0093】 [Manufacturing Example 1] (Manufacturing of CNT Forests) Two wafers coated with a catalyst for CNT growth were prepared, and vertically oriented CNTs were grown from the catalyst by chemical vapor deposition to produce a total of two sets of vertically oriented CNT forests oriented perpendicular to the wafers. The CNTs constituting the CNT forests were multi-walled carbon nanotubes, with an average length of 250 μm per tube, an average diameter of 6 to 10 nm, a carbon purity of 99.8% or higher, and a crystallinity (D / G ratio) of 0.6 to 0.8. 【0094】 [Example 1] As the glass fiber, a quartz glass fiber (length 52 m, diameter 125 μm) with a surface not coated with resin or the like was used. A cylindrical object with an inner diameter of 6 cm was prepared, and the quartz glass fiber was passed through the inside of the cylindrical object. A substrate on which CNT forests were formed was placed on the inner wall surface of the cylindrical object so that each CNT forest faced the other. A CNT web was prepared by picking up the CNTs located at the ends of the CNT forest formed on the catalyst substrate with a picking tool and pulling them out in a sheet-like manner. The pulled-out portion was then brought into contact with the quartz glass fiber, and bundles of multiple CNT fibers constituting the CNT web were attached to it. 【0095】A cylindrical object was rotated at 30 rpm to wrap CNT fibers around the surface of a quartz glass fiber, and the quartz glass fiber with the wrapped CNT fibers was then wound up on a rotating roll with a diameter of 20 cm. The winding speed of the rotating roll was 11.7 mm / min. The quartz glass fiber was not rotated around its length (rotation of the fiber itself). As a result, the CNT fibers wrapped around the outer circumference of the surface of the quartz glass fiber, coating it. After coating with CNT fibers and before winding with the rotating roll, ethanol was sprayed and then vaporized to obtain a 50 m long carbon nanotube coated optical fiber (1). The orientation angle between the CNT fibers and the quartz glass fiber in the carbon nanotube coated optical fiber (1) was approximately 45°. The thickness of the CNT fiber layer covering the surface of the quartz glass fiber was observed to be approximately 6 μm (5.8–6.5 μm) by SEM. 【0096】 [Heat Resistance Evaluation] An LC connector was attached to one end of a carbon nanotube coated optical fiber (1), and the LC connector was connected to an optical fiber measuring instrument. The carbon nanotube coated optical fiber (1) was fixed to a heat-resistant metal plate measuring 3600 mm in length and 300 mm in width using a carbon nanotube ribbon, as shown in Figure 5, and the metal plate was placed in an electric tubular furnace. In Figure 5, L1 was 800 mm, L2 was 1600 mm, L3 was 1200 mm, and L4 was 1400 mm. The tubular furnace was evacuated, the temperature of the tubular furnace was set to 750°C, and it was heated for 4 hours. During heating, the temperature was measured using the carbon nanotube coated optical fiber (1). The OFDR method was used for temperature measurement. Temperature measurement points were set at 2.6 mm intervals on the carbon nanotube coated optical fiber (1), and the temperature measurement speed was set to 8 Hz. 【0097】Even when the carbon nanotube-coated optical fiber (1) was heated as described above, temperature measurements could be performed without interruption. This confirmed that the carbon nanotube-coated optical fiber (1) was not broken. When the carbon nanotube-coated optical fiber (1) was removed after heating and bent to reduce its radius of curvature, it did not break. This confirmed that the carbon nanotube-coated optical fiber (1) had high bending strength even after heating. When an uncoated quartz glass fiber was heated in the same manner as above and bent to reduce its radius of curvature, the quartz glass fiber broke and did not have bending resistance. 【0098】 Similarly, when the inside of the tubular furnace was replaced with nitrogen, hydrogen, or acetylene, the carbon nanotube-coated optical fiber (1) did not break and maintained high bending strength even after heating. 【0099】 Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various omissions, substitutions, modifications, and changes are possible within the scope of the gist of the present invention as described in the claims. These embodiments and their variations are included in the scope and gist of the invention, as well as in the scope of the invention and its equivalents as described in the claims. 【0100】 1...CNT-coated optical fiber 2...Optical fiber 4...CNT fiber layer 6...Bundle of CNT fibers spirally coating the optical fiber 8...Centerline of the bundle of CNT fibers spirally coating the optical fiber 10...CNT substrate 11...Substrate 12...CNT forest 20...CNT web drawn from the CNT forest 22...CNT fibers constituting the CNT web 40...Metal plate 50...Carbon nanotube-coated optical fiber (1) 60...LC connector

Claims

1. A carbon nanotube coated optical fiber comprising an optical fiber and a carbon nanotube fiber layer covering the surface of the optical fiber.

2. The carbon nanotube coated optical fiber according to claim 1, wherein the thickness of the carbon nanotube fiber layer is 1 to 50 μm.

3. The carbon nanotube coated optical fiber according to claim 1, wherein the optical fiber is a silica glass fiber.

4. An optical fiber sensing device comprising a carbon nanotube-coated optical fiber as described in claim 1.

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